Use a prepaid Micro-sim to make phone calls with this watch, 2g GSM :850/900/1800/1900Mhz bands, Good for T-Mobile, Straight Talk, Simple Mobile, or any other carrier that accepts a 2G GSM Sim Card. Will NOT work with 3G only providers like ATT, Will NOT work with any CDMA Carriers such as Verizon, Sprint, Boost, PagePlus etc.

Support android 4.0 or above versions and iOS 8.0 or above versions, for Iphone series, it only supports partial features such as Pedometer, Calendar, Call Sync, Calculator, Clock, Stopwatch, Music player control, handsfree etc.